Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $237.34   7.804%   $255.862   $255.86   $255.85   $255.90  
  Purchase #2 $62.82   12.819%   $70.8729   $70.87   $70.85   $70.90  
  Purchase #3 $27.90   8.615%   $30.3036   $30.30   $30.30   $30.30  
  Purchase #4 $174.96   7.340%   $187.8021   $187.80   $187.80   $187.80  
  Purchase #5 $119.60   5.660%   $126.3694   $126.37   $126.35   $126.40  
  Purchase #6 $99.83   10.495%   $110.3072   $110.31   $110.30   $110.30  
  Purchase #7 $226.72   11.191%   $252.0922   $252.09   $252.10   $252.10  
  7 purchase totals = $949.17       $1,033.6094   $1,033.60   $1,033.55   $1,033.70